ACPAtmospheric Chemistry and PhysicsACPAtmos. Chem. Phys.1680-7324Copernicus PublicationsGöttingen, Germany10.5194/acp-7-5061-2007Global model simulations of the impact of ocean-going ships on aerosols, clouds, and the radiation budgetLauerA.1EyringV.1HendricksJ.1JöckelP.2LohmannU.31DLR-Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany2Max Planck Institute for Chemistry, Mainz, Germany3Institute of Atmospheric and Climate Science, Zurich, Switzerland0410200771950615079This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.This article is available from http://www.atmos-chem-phys.net/7/5061/2007/acp-7-5061-2007.htmlThe full text article is available as a PDF file from http://www.atmos-chem-phys.net/7/5061/2007/acp-7-5061-2007.pdf

International shipping contributes significantly to the fuel consumption of
all transport related activities. Specific emissions of pollutants such as
sulfur dioxide (SO<sub>2</sub>) per kg of fuel emitted are higher than for road
transport or aviation. Besides gaseous pollutants, ships also emit various
types of particulate matter. The aerosol impacts the Earth's radiation
budget directly by scattering and absorbing the
solar and thermal radiation and
indirectly by changing cloud properties. Here we use ECHAM5/MESSy1-MADE, a
global climate model with detailed aerosol and cloud microphysics to study the climate impacts of international shipping.
The simulations show that emissions from ships significantly increase
the cloud droplet number concentration of low marine water clouds
by up to 5% to 30% depending on the ship
emission inventory and the geographic region.
Whereas the cloud liquid water
content remains nearly unchanged in these simulations, effective radii of
cloud droplets decrease, leading to cloud optical thickness increase
of up to
5&ndash;10%. The sensitivity of the results is estimated by using three
different emission inventories for present-day conditions. The sensitivity
analysis reveals that shipping contributes to 2.3% to 3.6% of the
total sulfate burden and 0.4% to 1.4% to the total black carbon burden
in the year 2000
on the global mean.
In addition to changes in aerosol chemical composition,
shipping increases the aerosol number concentration, e.g. up to 25% in
the size range of the accumulation mode (typically &gt;0.1 μm) over the
Atlantic. The total aerosol optical thickness over the Indian Ocean, the
Gulf of Mexico and the Northeastern Pacific increases by up to 8&ndash;10%
depending on the emission inventory. Changes in aerosol optical thickness
caused by shipping induced modification of aerosol particle number
concentration and chemical composition lead to a change
in the
shortwave
radiation budget at the top of the atmosphere (ToA) under
clear-sky condition
of about &minus;0.014 W/m² to
&minus;0.038 W/m² for a global annual average.
The corresponding all-sky direct aerosol forcing ranges between
&minus;0.011 W/m² and &minus;0.013 W/m².
The indirect aerosol effect of ships on
climate is found to be far larger than previously estimated. An indirect
radiative effect of &minus;0.19 W/m² to &minus;0.60 W/m²
(a change in the atmospheric shortwave radiative flux at ToA)
is calculated here, contributing
17% to 39% of the total indirect effect of anthropogenic aerosols.
This contribution is high because ship emissions are released in regions
with frequent low marine clouds in an otherwise clean environment. In
addition, the potential impact of particulate matter on the radiation budget
is larger over the dark ocean surface than over polluted regions over land.